1. Field of the Technology
The present technology relates to a rotation driving force transmitting member, a photoreceptor drum, a process cartridge, and an image forming apparatus.
2. Description of the Related Art
A duplicator, a printer, a facsimile machine, or the like includes an image forming apparatus which forms an image using electrophotography. In the electrophotographic image forming apparatus, a electrostatic latent image is formed on a surface of a photoreceptor drum by a charging section and a exposure section, the electrostatic latent image is developed due to supply of a toner by a developing section, a toner image on the surface of the photoreceptor drum is transferred to a recording medium such as a recording sheet by a transfer section, the toner image is fixed on the recording sheet by a fixing section, and the image is formed.
A rotation driving force from a motor or the like, which is provided in the image forming apparatus, is transmitted to the photoreceptor drum via a rotation driving force transmitting member such as gears or coupling members. Therefore, the photoreceptor drum is constituted so as to be rotated around an axial line thereof. In addition, in a process cartridge described in Japanese Unexamined Patent Publication JP-A 62-65049 (1987), members other than the photoreceptor drum in the process cartridge as well as the photoreceptor drum are constituted so as to be rotated by the motor and the like which is provided in the image forming apparatus. Here, in the process cartridge, the photoreceptor drum, the charging section, the developing section, and the like are integrally constituted as one cartridge. Therefore, for example, a developing roller included in the developing section is also rotated as the photoreceptor drum is rotated.
In Japanese Examined Patent Publication JP-B2 2875203 and Japanese Unexamined Patent Publication JP-A 10-104905 (1998), a rotation driving force transmitting member is described. The rotation driving force transmitting member includes: a driving rotation body which is rotated by a rotation driving force of a motor, and in the center portion thereof, a concave portion, which has a polygonal cross-section and is twisted, is formed; and a convex portion that is provided in one end in a longitudinal direction of a photoreceptor drum, fitted in the concave portion of the driving rotation body, has a polygonal cross-section, and is twisted. Due to rotation of the driving rotation body in a state where the concave portion and the convex portion are fitted in each other, the rotation driving force transmitting member is constituted so that a rotation driving force of the motor is transmitted to the photoreceptor drum via the driving rotation body and the convex portion in a state where the convex portion is subjected to a drawing force toward the concave portion side.
In the rotation driving force transmitting members described in JP-B2 2875203 and JP-A 10-104905, even though a centroid of the polygonal cross-section of the convex portion is misaligned with a centroid of the polygonal cross-section of the concave portion in a state before the concave portion starts rotation, if the concave portion starts rotation, the tips of the corners of the polygonal cross-section of the convex portion abut against the side portions of the polygonal cross-section of the concave portion due to a drawing force between the concave portion and the convex portion, and the two centroids are aligned with each other. As a result, it is possible to rotate the photoreceptor drum provided with the convex portion without eccentricity.
However, the rotation driving force transmitting members which are described in JP-B2 2875203 and JP-A 10-104905 have the following problems. That is, due to the impact when the concave portion starts rotation and the tips of the corners of the polygonal cross-section of the convex portion abut against the side portions of the polygonal cross-section of the concave portion, the tips of the corners are easily damaged. In addition, the tips of the corners of the polygonal cross-section of the convex portion are easily damaged even when the convex portion and the concave portion are fitted in each other. Moreover, if the tips of the corners of the polygonal cross-section of the convex portion is damaged, for example, even though the damage is minute, the abutment positions between the polygonal cross-section of the convex portion and the polygonal cross-section of the concave portion are misaligned, and the centroid of the polygonal cross-section of the convex portion is misaligned with the centroid of the polygonal cross-section of the concave portion. Therefore, a backlash occurs in rotation of the photoreceptor drum.